Electrically controlled variable thickness plate

ABSTRACT

The invention refers to electrically controlled optical switching devices which are based on the use of a layer of dielectric and transparent viscoelastic material (G) located between transparent first (ES 1 ) and transparent second (ES 2 ) electrode structures. According to the invention, the first (ES 1 ) and second (ES 2 ) electrode structures are arranged in a manner that the thickness of the layer of the viscoelastic material (G) can be electrically altered maintaining the thickness of said layer substantially equal. This makes it possible to realize a generic, electrically controlled variable thickness plate ( 30 ). The generic variable thickness plate ( 30 ) can be further used to create optical switching devices based on a Fabry Perot Interferometer or a Mach-Zehnder Interferometer.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an electrically switchable opticaldevice operating in transmission for manipulating an incident light waveor light waves passing through the device. The invention also relates toa method for forming electrically switchable optical devices for formingsuch an optical switching device.

2. Discussion of Related Art

Optical signals in different forms are today increasingly utilized inmany different types of devices and applications. In order to take fulladvantage of systems including optical signals or beams, it must bepossible to direct the optical signal or beam coming in on a guidedoptical conduit, or on some other type of optical system in a desiredelectrically controlled manner to another optical conduit or to anotheroptical system. The aforementioned optical conduit can be, for example,an optical fiber or other type of optical waveguide. There exists a widevariety of optical systems, which work under fast changing operationalconditions, and thus require capability to perform optical functions inan efficient and electrically controlled manner.

Especially the recent rapid development of optical telecommunication andoptical data processing systems creates increasing needs for versatileelectrically switchable optical devices.

In addition to the act of simply switching the optical signal/beam on oroff, the term “optical switching” above and hereinbelow also refers tomore complex optical functions, i.e. transformations of the opticalsignal/beam and/or its path. These include, for example, dividing,redirecting or modulating the amplitude or phase of the opticalsignal/beam in a desired manner.

In the following, some prior art solutions for electrically controlledoptical switching are shortly discussed. However, methods which arebased on first converting optical signals into electrical signals forswitching and then reconverting said electrical signals back intooptical signals for outputting are not included in the followingdiscussion as they are not relevant to the present invention.

A conventional method for electrically controlled optical switching isto mechanically move the optical components, for example mirrors,beamsplitters or beam attenuators in order to affect the propagation ofthe optical signal/beam. Said mechanical movements can be realized usingvarious kinds of electrical actuators. However, such optical componentstogether with the required electrical actuators cannot be easily madevery compact in size and they are also rather difficult and expensive tomanufacture, especially as mass-produced articles.

Silicon-surfacemicromachining is a recent technology for fabricatingminiature or microscopic devices. This technology has also been used formanufacturing optical microelectromechanical systems (optical MEMS).

U.S. Pat. No. 5,867,297 discloses an oscillatory optical MEMS deviceincluding a micromirror for deflecting light in a predetermined manner.Small physical sizes and masses of these micromachined silicon “machineparts” make them more robust and capable of faster operation thanconventional macroscopic mechanical devices.

Grating Light Valve™ devices by Silicon Light Machines, USA representanother type of optical MEMS devices. U.S. Pat. No. 5,311,360 disclosesa light modulator structure, which consists of parallel rows ofreflective ribbons. Alternative rows of ribbons can be pulled down byelectrostatic attraction forces a distance corresponding toapproximately one-quarter wavelength to create an electricallycontrolled grating like structure, which can be used to diffractivelymodulate the incident light wave. The electrical switching of theribbons can be realized by integrating bottom electrodes below theribbons, and by applying different voltages to the ribbons and saidbottom electrodes to create the required electrostatic forces. U.S. Pat.No. 6,130,770 discloses another type of solution, where instead of usingphysical electrical connections to charge the predetermined ribbons ofthe light modulator structure, selected ribbons are electrically chargedwith an electron gun.

In principle, silicon optical MEMS technology uses processing stepsderived from the integrated circuit (IC) fabrication techniques ofphotolithography, material deposition and chemical etching to producethe movable mechanical structures on a silicon chip. The aforementionedmanufacturing process is, however, fairly difficult and thus expensive.Further, the optical MEMS devices operate mainly only in reflection andthus the capabilities of such devices of more complex transformations ofthe optical signal/beam and/or its path are limited. Material fatiguemay also become significant in certain applications.

Birefringence, also known as double refraction, is a property which canbe found in some transparent materials, for example in crystals. Suchoptical materials have two different indices of refraction in differentdirections. This can be used to create Pockels effect, anelectro-optical effect in which the application of an electric fieldproduces a birefringence which is proportional to the electric fieldapplied to the material. The Pockels effect is well known in the art andit is commonly used to create, for example, fast optical shutters.However, because the use of birefringence requires use of polarizedlight, this severely limits its use as a general method in realizingoptical switching devices.

U.S. Pat. No. 5,937,115 describes switchable optical componentstructures based on a holographic polymer dispersed liquid crystal.These are electronically controlled Bragg grating structures which allowto electronically switch on and off the diffractive effect of thetransparent grating structures, which have been optically recorded orotherwise generated in the material. These electronically switchableBragg grating (ESBG) devices can be used for various filtering orlensing applications. The major drawback of the ESBG technology is thecomplex manufacturing process required. Environmental concerns andhazards generally related to liquid crystal materials apply also to theESBG devices.

U.S. Pat. No. 4,626,920 discloses a semiconductor device, which has anarray of spaced charge storage electrodes on semiconductor material (Si)and an elastomer layer disposed on said electrodes. At least oneconductive and light reflective layer is disposed over the elastomerlayer. When voltages are applied between the charge storage electrodesand the conductive layer, this causes the deformation of theconductive/reflective layer and the elastomer layer from a flat surfaceto a form having a sinusoidally cyclically varying cross-section. Thus,the reflective front surface of the conductive layer can be utilized asan electrically switchable reflective grating.

GB patent 2,237,443 describes another light modulating device, where areflective elastomer or viscoelastic layer is utilized for lightmodulation. In this arrangement an electron gun (cathode ray tube) isused instead of direct electrical connections/electrodes (cf. U.S. Pat.No. 4,626,920) to generate the electrical pattern needed to deform theelastomer layer.

An important aspect in the above described type of systems (U.S. Pat.No. 4,626,920 and GB 2,237,443) is the operation of theconductive/reflective layer or layers which is/are mounted on thedeformable elastomer layer. Said conductive/reflective layer or layersmust reliably and repeatably provide precise patterns of deformationswhich correspond to the charge pattern modifying the elastomer layer.This, together with the fact that said devices operate only inreflection, limits the use of such devices due to the limited selectionof suitable conductive and reflective materials as well as due to theoverall response characteristics (sensitivity to the appliedvoltages/charges, temporal response characteristics) of the device.

Yury P. Guscho “Physics of Reliofography” (Nauka, 1992, 520 p. inRussian) describes in chapter 7 a number of light modulator structures,in which a transparent viscoelastic layer is electrically deformed tomanipulate the light passing through said viscoelastic layer. Thesedevices can be taken to present the closest prior art with respect tothe current invention, and they are therefore shortly described belowwith reference to the appended FIGS. 1 a and 1 b.

FIGS. 1 a and 1 b correspond to FIG. 7.1 in chapter 7 of “Physics ofReliofography” and show the two basic schemes of the light modulatorstructures.

In the first scheme in FIG. 1 a, the driving signal (U) for deformingthe viscoelastic layer G is applied from the free side of theviscoelastic layer G using driving electrodes ES1, which electrodes ES1are formed on the lower surface of a top glass substrate SM1. A gap isleft between the free surface of the viscoelastic layer G and the lowersurface of the top glass substrate SM1, allowing the viscoelastic layerG to deform without contacting the opposite structure. Theaforementioned gap can be for example air, gas or vacuum. The electricfield deforming the viscoelastic layer G is generated between thedriving electrodes ES1 and the conductive substrate electrode ES2.

In the second scheme in FIG. 1 b, the viscoelastic layer G is disposedon the driving electrode structure ES1, which in turn is formed on aglass substrate SM1. The electric field deforming the viscoelastic layerG is generated by applying alternating voltages to the neighbouringelectrode zones in the driving electrode structure ES1.

In both of the aforementioned schemes, the free surface of theviscoelastic layer G can be coated with a conductive reflecting layer(sputtered metal film).

According to our best understanding, all the light modulator structurespresented in the chapter 7 of “Physics of Reliofography” and discussedshortly above are based on the basic idea of deforming the viscoelasticlayer into a surface structure having a substantially sinusoidallyvarying cross-section. This allows to use the viscoelastic layer as anelectrically controlled sinusoidal grating in order to modulate theincident light wave.

DISCLOSURE OF INVENTION

The main purpose of the present invention is to produce a novel devicefor optical switching, which is based on the use of an electricallydeformable viscoelastic layer in order to manipulate the light passingthrough said viscoelastic layer, but which is not based on using theviscoelastic layer as a grating-like structure. This innovation allowingto manipulate the viscoelastic layer in a completely new waysignificantly broadens the possibilities to use electrically controlledviscoelastic materials for optical switching applications.

According to a first aspect of the present invention, an opticalswitching device operating in transmission for manipulating an incidentlight wave or light waves passing through the device comprises at leasta first transparent electrode structure comprising one or more electrodezone/s having an effective total area A₁ and arranged in a manner thatthe electrode zone/s is/are capable of receiving voltage or voltages, asecond transparent electrode structure comprising one or more separateelectrode zone/s having effective total area A₂ and arranged in a mannerthat the electrode zone/s is/are capable of receiving voltage orvoltages, and a layer of dielectric and transparent viscoelasticmaterial located between the first and the second electrode structurescapable of being deformed in local thickness in response to electricfield/s generated by the first and the second electrode structures andthe electric field/s passing through the viscoelastic material, whereinthe first and the second electrode structures are arranged in a mannerthat the effective total area A₁ of the first electrode structure issubstantially larger than the effective total area A₂ of the secondelectrode structure, and within the area corresponding substantially tothe projection of said area A₂ to the area A₁, the thickness of thelayer of the viscoelastic material can be electrically alteredmaintaining the thickness of the layer in different parts of theprojection area substantially equal in order to realize an electricallycontrolled variable thickness plate, so that the variable thicknessplate is suitable for altering the optical path length of thetransmitted light in order to perform optical switching based oninterferometry.

According to a second aspect of the present invention, a method forforming an optical switching device operating in transmission formanipulating an incident light wave or light waves passing through saiddevice, said method comprises at least the steps of forming a firsttransparent electrode structure comprising one or more electrode zone/shaving effective total area A₁ and arranged in a manner that saidelectrode zone/s is/are capable of receiving voltage or voltages,forming a second transparent electrode structure comprising one or moreseparate electrode zone/s having effective total area A₂ and arranged ina manner that the electrode zone/s is/are capable of receiving voltageor voltages, and forming a layer of dielectric and transparentviscoelastic material between the first and the second electrodestructures capable of being deformed in local thickness in response toelectric field/s generated by the first and the second electrodestructures and the electric field/s passing through the viscoelasticmaterial, wherein the first and the second electrode structures arearranged in a manner that the effective total area A₁ of the firstelectrode structure is substantially larger than the effective totalarea A₂ of the second electrode structure, and within the areacorresponding substantially to the projection of the area A₂ to the areaA₁, the thickness of the layer of viscoelastic material can beelectrically altered maintaining the thickness of the layer in differentparts of the projection area substantially equal in order to realize anelectrically controlled variable thickness plate, so that the variablethickness plate is suitable for altering the optical path length of thetransmitted light in order to perform optical switching based oninterferometry.

The invention also relates to a method for forming electricallyswitchable optical devices. The method according to the invention isprimarily characterized in what will be presented in the characterizingpart of the independent claim 9.

The basic idea of the invention is to provide a device, in which thetransparent viscoelastic layer located between opposite transparentelectrode structures can be deformed in such a way that the thickness ofsaid viscoelastic layer can be electrically altered while simultaneouslymaintaining the substantially flat surface of the viscoelastic layerinside a certain area defined by the electrode structures. Due to thefact that the viscoelastic material has a different index of refractioncompared to the medium forming the necessary gap between theviscoelastic layer and at least one of the opposite electrodestructures, the light passing through the viscoelastic layer and saidgap experiences a different optical path length depending on thethickness of the viscoelastic layer. Therefore, the optical deviceaccording to the invention can be used as a generic electricallycontrolled variable thickness plate, which can be used to alter thephase of the light passing through the device.

In one specific embodiment of the invention, the opposite electrodestructures and/or substrate materials supporting said structures in thevariable thickness plate device are realized as light reflectingstructure/s. This causes the light entering the device to pass throughthe viscoelastic layer more than once and thus makes it possible tocreate an electrically controlled Fabry Perot Interferometer.

In another embodiment of the invention, the variable thickness platedevice is placed into the optical path of one of the optical arms of aMach-Zehnder Interferometer. This makes it possible to create anelectrically controlled Mach-Zehnder Interferometer type opticalswitching device. Preferably, and differing from the case of theaforementioned Fabry Perot switch, all the stationary optical surfacesof the variable thickness plate are arranged to have anti-reflectioncoatings.

The electrically controlled variable thickness plate and the variousapplications utilizing the same can be used for many types of opticalswitching purposes. The devices according to the invention can be used,for example, to switch a beam of light with a given wavelength λ on oroff, or they can be used as variable intensity filters to adjust theintensity of the transmitted beam. The Mach-Zehnder Interferometerswitch makes it possible to switch the optical signal between severaltargets and/or to create any desired ratio of the optical signals atsaid targets.

The devices according to the invention are significantly moreadvantageous than prior art devices in providing much widerpossibilities to manufacture electrically controlled optical switchingdevices. The manufacture of such devices also promises to be relativelyeasy and economical compared to prior art technologies allowing, forexample, the use of a wider variety of substrate materials and simplermanufacturing processes. The manufacture of the devices according toinvention do not involve for example the use of environmentally harmfulliquid crystal materials, or require deep etching. Further, the opticalswitching devices according to the invention are independent ofpolarization.

The preferred embodiments of the invention and their benefits willbecome more apparent to a person skilled in the art through thedescription and examples given hereinbelow, and also through theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in more detail withreference to the appended drawings, in which

FIGS. 1 a, 1 b illustrate prior art light modulator structures utilizingan electrically controlled transparent viscoelastic layer to producesinusoidally varying gratings,

FIG. 2 illustrates the behaviour of dielectric liquid in an electricfield between electrode plates of a field capacitor,

FIG. 3 illustrates schematically a generic variable thickness plateaccording to the invention,

FIG. 4 illustrates schematically a Fabry Perot Interferometer accordingto the invention, and

FIG. 5 illustrates schematically a Mach-Zehnder Interferometer typeswitch according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

It is to be understood that the drawings presented hereinbelow aredesigned solely for purposes of illustration and thus, for example, notfor showing the various components of the devices in their correctrelative scale and/or shape. For the sake of clarity, the components anddetails which are not essential in order to explain the spirit of theinvention have also been omitted in the drawings.

FIG. 2 illustrates the general principle of physics, which can beobserved with dielectric substances. A dielectric substance can bedefined as a substance in which an electric field may be maintained withzero or near zero power dissipation, i.e. the electrical conductivity iszero or near zero. In an electric field, the surface of two dielectricswith different dielectric constants is known to experience a force whichis proportional to the square of the electric field strength. In FIG. 2where an electric field is formed between electrode plates 20 and 21 ofa field capacitor by applying suitable voltages V₁ and V₂ on saidelectrodes, dielectric liquid 22 is drawn between the electrode platesbecause of the aforementioned force effect.

FIG. 3 illustrates schematically generic variable thickness plate 30according to the invention. A layer of dielectric and viscoelastictransparent material G is applied onto a first transparent electrodestructure ES1, which in turn is formed on a first transparent substratematerial SM1. Said first electrode structure ES1 comprises a singleelectrode zone having an effective total area A₁ and coveringsubstantially the whole area (≈A₁) of the first substrate material SM1.A second transparent electrode structure ES2 having an effective totalarea A₂ is formed on a second transparent substrate material SM2. Saidsecond electrode structure ES2 is located at a distance from theviscoelastic layer G so that the viscoelastic layer G is located betweenthe first ES1 and the second ES2 electrode structures. The secondelectrode structure ES2 also comprises a single electrode zone, butinstead of covering the total area of the second substrate material SM2(and that of the viscoelastic material G), the second electrodestructure/zone ES2 is arranged to cover only a part of said area. Thismakes it possible to change the thickness of the viscoelastic layer Gbelow the second electrode structure/zone ES2 as a function of thevoltage applied between first and second electrode structures in such amanner that the viscoelastic layer G maintains a substantially flatsurface and therefore an even thickness below the second electrodestructure/zone ES2. In order to allow the viscoelastic layer G to deformwithout contacting the opposite electrode structure ES2, a gap A is leftbetween the surface of the viscoelastic layer G and said electrodestructure ES2.

Due to the fact that the viscoelastic material G has a different indexof refraction compared to the medium forming the aforementioned gap A,the light passing through the variable thickness plate device 30 withinthe area (≈A₂) defined by the projection of the second electrodestructure ES2 onto the first electrode structure ES1 experiences adifferent optical path length depending on the thickness of theviscoelastic layer G.

A suitable transparent viscoelastic material G includes, for example,silicone gel, oil, various polymer materials or other viscous substancesthat have a tendency to deform when placed in a presence of an electricfield, and said materials relax towards their original form or shapeafter the aforementioned effect ceases.

The gap A between the viscoelastic layer G and at least one of theopposite electrode structures ES1,ES2 can be for example air, gas orvacuum.

In order not to significantly change the density of the viscoelasticmaterial G when changing the thickness of the layer of said materialbetween the first ES1 and the second ES2 electrode structures, the areaof the projection of the smaller electrode structure (ES2 with effectivetotal area A₂) to the larger electrode structure (ES1 with effectivetotal area A₁) is arranged to be smaller than the area of the freesurface of the viscoelastic layer G. In other words, in the presence ofan electric field between said electrodes, the viscoelastic layer Goutside the aforementioned projection area becomes thinner when theamount of viscoelastic material in that area decreases, andrespectively, within said projection area (≈A₂), the viscoelastic layerG grows thicker when the amount of viscoelastic material builds up.

The transparent electrode structure ES1 and/or ES2 is preferably made ofindium tin oxide (ITO), as is known in the art, and the transparentsubstrates SM1,SM2 supporting said electrode structures are preferablymade of glass. Other methods for creating substantially transparentelectrode structures on any substantially transparent substrate materialcan also be employed without departing from the scope of the presentinvention.

Instead of being fully transparent, it is possible that the substratematerials SM1,SM2 and/or the electrode structures ES1,ES2 on either sideof the viscoelastic layer G may be arranged to provide spectralfiltering of the transmitted light.

It is obvious that the light B incident to the variable thickness plate30 can enter the device from either side, for example, through the firstsubstrate material SM1 or through the second substrate material SM2.

Hereinbelow, some specific examples of different types ofinterferometric optical switching devices utilizing the variablethickness plate 30 according to the invention will be presented. Itshould be understood that these examples should not be interpreted as adefinition of the limits of the invention. Various other kinds ofoptical structures can also be realized according to the invention andwithin the limits of the appended claims practising the normal designcapabilities of a person skilled in the art.

Fabry Perot Interferometer

Fabry Perot Interferometer (FPI) is a well-known device in the art. Inprinciple and in its simplest form, the device comprises two planar,parallel, highly reflecting surfaces separated by a distance d so thatthese reflecting surfaces (mirrors) form a cavity between them. When anFPI cavity is illuminated at normal incidence through either of saidsurfaces (end mirrors) with light having a wavelength of λ, the FPIpasses the light through only if the optical path difference (OPD) of adirectly transmitted beam (with effective pathlength d) and a beamreflected back and forward between the aforementioned reflectingsurfaces (with effective pathlength 2 d, 4 d, 6 d . . . ) equals mλ,where m is an integer. In other words, in order for the light to passthrough the FPI, said directly transmitted beam and said reflected beamneed to be subjected to constructive interference. Slight detuning ofthe OPD will result in a suppression of the light transmitted throughthe FPI cavity by a factor which is determined by the so-called finesseof the FPI cavity. The aforementioned effect is well-known in the artand utilized in different types of spectroscopic applications.

By using the variable thickness plate 30 according to the invention andillustrated in FIG. 3, one can realize an FPI cavity which allows tocontrol the OPD of the cavity by simply varying the voltage across thefirst ES1 and second ES2 electrode structures and thus changing thethickness of the viscoelastic layer G. One example of a Fabry Perotcavity 40 based on this principle is schematically illustrated in FIG.4.

In order to provide the reflecting surfaces for the FPI cavity, thefirst SM1 and second SM2 substrate materials and/or the first ES1 andsecond ES2 electrode structures are arranged to be reflecting. Onepossibility is to coat the surfaces of the first SM1 and second SM2substrate materials with highly reflective optical coatings RC1 and RC2,respectively. Methods for manufacturing such coatings on transparentmaterials are well known in the art.

The FPI cavity can also be formed by locating the variable thicknessplate structure 30 between two external mirrors.

A Fabry Perot cavity 40, which is realized in the aforementioned manner,can be used to switch a beam of light with a given wavelength λ on oroff (OPD is detuned significantly off), or it can be used as a variableintensity filter to adjust the intensity of the transmitted beam (OPD isdetuned only slightly off). The Fabry Perot cavity 40 can be usedfurther for wavelength filtering if it is illuminated with light Bhaving discrete wavelengths, for example certain laser generatedwavelength bands, or even more continuous spectrum. In this case, theFabry Perot cavity 40 allows transmission only for those wavelengthswhich fulfil the aforementioned OPD-criterion.

Mach-Zehnder Interferometer-type Switch

The variable thickness plate 30 according to the invention andillustrated in FIG. 3 can also be utilized in other types ofinterferometric devices than the aforementioned Fabry Perot cavity 40.

FIG. 5 illustrates an optical switch 50 based on a Mach-ZehnderInterferometer (MZI). By using a first beamsplitting means 53, a lightbeam B entering the MZI is divided into separate first 51 and second 52beams, which beams are directed into corresponding separate optical armsof the MZI. Mirrors 54 and 55 are arranged to direct the first 51 andsecond 52 beams, respectively, towards a second beamsplitting means 56.In the second beamsplitting 56 means, the first beam 51 is furtherdivided into two beams: one directed towards a target 57 and the otherone towards a target 58. Correspondingly, the second beam 52 is dividedby the second beamsplitting means 56 into two beams: one directedtowards the target 57 and the other one towards the target 58.

Depending on the OPD undergone by the first 51 and the second 52 beamstravelling through the separate arms of the MZI and in cases where saidOPD equals mλ/2 (m is an integer), there can be constructiveinterference of said beams taking place at the target 57 (lighttransmitted) and destructive interference at the target 58 (no lighttransmitted), or vice versa. In case the OPD deviates from mλ/2, someintermediate light intensity will be detected at both of the targets 57and 58.

In prior art interferometric devices utilizing an MZI, the variablephase delay, i.e. the alteration of the OPD experienced by the the first51 and the second 52 beams has been typically realized by moving one ofthe mirrors 54,55 included in the two optical arms of the interferometersetup.

In a Mach-Zehnder switch 50 according to the invention, the alterationof the OPD is realized by introducing the variable thickness plate 30(FIG. 3) in one of the two arms of the MZI device. In FIG. 5, thevariable thickness plate 30 is illustrated as being introduced into thefirst beam 51 after the first beamsplitting means 53. Alternatively, thevariable thickness plate 30 could be introduced in any location in thefirst 51 or in the second 52 beam between the first 53 and the second 56beamsplitting means. Preferably, and deviating from the case of theaforementioned Fabry Perot cavity 40, all the stationary opticalsurfaces of the variable thickness plate 40 are arranged to haveanti-reflection coatings.

The Mach-Zehnder switch 50 according to the invention allows theswitching of the signal between targets 57 and 58 and/or the formationof any desired ratio of the signals at said targets. This can beachieved simply by applying a suitable voltage on the first ES1 and thesecond ES2 electrode structures of the variable thickness plate 30 (FIG.3). For a person skilled in the art, it is also obvious that in a mannersimilar to the aforementioned Fabry Perot switch 40, the Mach-Zehnderswitch 50 can also be used for wavelength filtering purposes. Targets 57and 58 can be, for example, detectors or entrance apertures of opticalconduits or other optical systems.

While the invention has been shown and described above with respect toselected types of optical switching devices, it should be understoodthat these devices are only examples and that a person skilled in theart could construct other optical switching devices utilizing techniquesother than those specifically disclosed herein while still remainingwithin the spirit and scope of the present invention. It shouldtherefore be understood that various omissions and substitutions andchanges in the form and detail of the switching devices illustrated, aswell as in the operation of the same, may be made by those skilled inthe art without departing from the spirit of the invention. For example,it is expressly intended that all combinations of those elements whichperform substantially the same function in substantially the same way toachieve the same results are within the scope of the invention.Moreover, it should be recognized that structures and/or elements shownand/or described in connection with any disclosed form or embodiment ofthe invention may be incorporated in any other disclosed or described orsuggested form or embodiment as a general matter of design choice. It isthe intention, therefore, to restrict the invention only in the mannerindicated by the scope of the claims appended hereto.

For example, the embodiments of the invention can be extended to deviceswhere either one or both of the first ES1 and/or second ES2 electrodestructures contain more than one electrode zone in order to ensure aneven thickness of the deformed viscoelastic layer G also in theperiphery of the projection area between the first ES1 and second ES2electrodes. In said periphery, the thickness of the viscoelastic layer Gtends to differ from the thickness in the center of the projection areabecause of uneven electric field strength, if only single electrode zonefirst ES1 and second ES2 electrode structures are used.

In case of an electrode structure (ES1 and/or ES2) comprising more thanone electrode zone, the expression “effective total area” of theelectrode structure used above and in the appended claims refers morespecifically to the area defined by the outside dimensions of theelectrode structure than simply to the integral area of the individualelectrode zones.

It will be evident for a person skilled in the art that the operation ofthe optical devices according to the invention relies on someapplications on optical interference, and thus requires a certain degreeof coherence and/or collimation of the optical signal/beam that is beingprocessed.

1. An optical switching device operating in transmission formanipulating an incident light wave or light waves (B) passing throughsaid device, comprising at least a first transparent electrode structure(ES1) comprising one or more electrode zone/s having an effective totalarea A₁ and arranged in a manner that said electrode zone/s is/arecapable of receiving voltage or voltages, a second transparent electrodestructure (ES2) comprising one or more separate electrode zone/s havingeffective total area A₂ and arranged in a manner that said electrodezone/s is/are capable of receiving voltage or voltages, and a layer ofdielectric and transparent viscoelastic material (G) located betweensaid first (ES1) and said second (ES2) electrode structures capable ofbeing deformed in local thickness in response to electric field/sgenerated by said first (ES1) and said second (ES2) electrode structuresand said electric field/s passing through said viscoelastic material(G), wherein said first (ES1) and said second (ES2) electrode structuresare arranged in a manner that the effective total area A₁ of said firstelectrode structure (ES1) is substantially larger than the effectivetotal area A₂ of said second electrode structure (ES2), and within thearea corresponding substantially to the projection of said area A₂ tosaid area A₁, the thickness of the layer of the viscoelastic material(G) can be electrically altered maintaining the thickness of said layerin different parts of said projection area substantially equal in orderto realize an electrically controlled variable thickness plate (30), sothat said variable thickness plate (30) is suitable for altering theoptical path length of the transmitted light (B) in order to performoptical switching based on interferometry.
 2. The device according toclaim 1 wherein said first (ES1) and second (ES2) electrode structureseach comprises a single, rectangular electrode zone and said electrodezones are arranged with planes thereof parallel to each other.
 3. Thedevice according to claim 1, wherein a substrate material (SM1)supporting said first electrode structure (ES1) and/or a substratematerial (SM2) supporting said second electrode structure (ES2) is/arearranged to provide spectral filtering of the transmitted light (B). 4.The device according to claim 1, wherein said first (ES1) and/or second(ES2) electrode structure/s is/are indium tin oxide (ITO) structure/s.5. The device according to claim 1, wherein stationary optical surfaces(ES1, ES2, SM1, SM2) of said device (30) are arranged to haveanti-reflection coatings.
 6. The device according to claim 1, whereinsaid device (30) is located between two external highly reflectingmirrors in order to perform an interferometric optical cavity.
 7. Thedevice according to claim 1, wherein substrate materials (SM1, SM2)supporting said first (ES1) and said second (ES2) electrode structures,and/or said first (ES1) and said second (ES2) electrode structures arearranged to be light reflecting (RC1, RC2) to form an interferometricoptical cavity in order to realize an electrically controlled FabryPerot Interferometer (40).
 8. The device according to claim 1, whereinsaid device (30) is placed into an optical path of at least one opticalarm of plural optical arms (51, 52) of a Mach-Zehnder Interferometer inorder to realize an electrically controlled Mach-Zehnder Interferometertype switch (50).
 9. A method for forming an optical switching deviceoperating in transmission for manipulating an incident light wave orlight waves (B) passing through said device, said method comprising atleast the steps of forming a first transparent electrode structure (ES1)comprising one or more electrode zone/s having effective total area A₁and arranged in a manner that said electrode zone/s is/are capable ofreceiving voltage or voltages, forming a second transparent electrodestructure (ES2) comprising one or more separate electrode zone/s havingeffective total area A₂ and arranged in a manner that said electrodezone/s is/are capable of receiving voltage or voltages, and forming alayer of dielectric and transparent viscoelastic material (G) betweensaid first (ES1) and said second (ES2) electrode structures capable ofbeing deformed in local thickness in response to electric field/sgenerated by said first (ES1) and said second (ES2) electrode structuresand said electric field/s passing through said viscoelastic material(G), wherein said first (ES1) and said second (ES2) electrode structuresare arranged in a manner that the effective total area A₁ of the firstelectrode structure (ES1) is substantially larger than the effectivetotal area A₂ of said second electrode structure (ES2), and within thearea corresponding substantially to the projection of said area A₂ tosaid area A₁, the thickness of the layer of viscoelastic material (G)can be electrically altered maintaining the thickness of said layer indifferent parts of said projection area substantially equal in order torealize an electrically controlled variable thickness plate (30), sothat said variable thickness plate (30) is suitable for altering theoptical path length of the transmitted light (B) in order to performoptical switching based on interferometry.
 10. The method according toclaim 9, wherein said first (ES1) and second (ES2) electrode structureseach comprises a single, rectangular electrode zone and said electrodezones are arranged with their planes being parallel to each other. 11.The method according to claim 9, wherein a substrate material (SM1)supporting said first electrode structure (ES1) and/or a substratematerial (SM2) supporting said second electrode structure (ES2) is/arearranged to provide spectral filtering of the transmitted light wave(B).
 12. The method according to claim 9, wherein said first (ES1)and/or second (ES2) electrode structure/s is/are formed as indium tinoxide (ITO) structure/s.
 13. The method according to claim 9, whereinstationary optical surfaces (ES1, ES2, SM1, SM2) of said device (30) arearranged to have anti-reflection coatings.
 14. The method according toclaim 9, wherein said device (30) is located between two external highlyreflecting mirrors in order to form an interferometric optical cavity.15. the method according to claim 9, wherein substrate materials (SM1,SM2) supporting said first (ES1) and said second (ES2) electrodestructures, and/or said first (ES1) and said second (ES2) electrodestructures are arranged to be light reflecting (RC1, RC2) to form aninterferometric optical cavity in order to realize an electricallycontrolled Fabry Perot Interferometer (40).
 16. The method according toclaim 9, wherein said device (30) is placed into an optical path of atleast one optical arm of plural optical arms (51, 52) of a Mach-ZehnderInterferometer in order to realize an electrically controlledMach-Zehnder Interferometer type switch (50).